The first year of self-employment usually contains one unpleasant surprise, and it arrives in April. You calculated income tax on your profit, set money aside for it, and then discovered a second tax you had never heard of that takes another 15.3%.
That tax is not a penalty for working for yourself. It is the part of your compensation an employer used to pay on your behalf, made visible for the first time.
What it actually is
Every W-2 employee in the United States pays FICA: 6.2% for Social Security and 1.45% for Medicare, withheld from their paycheck. What most employees never see is that their employer pays an identical 7.65% on top, out of the company's pocket, on the same wages.
When you are self-employed, there is no separate employer. You are both halves. So the combined rate is 12.4% for Social Security plus 2.9% for Medicare, which is the 15.3% figure. It is exactly the same total that was always being paid on a W-2 job — you simply used to see only half of it.
This matters when you set your rates. A $100,000 salary and $100,000 of freelance profit are not equivalent compensation, and the roughly 7.65 percentage points of employer-side tax is one of several reasons why.
The 92.35% factor
Self-employment tax is not applied to your full net profit. It applies to 92.35% of it.
The reasoning is a fairness adjustment. A W-2 employee never pays income tax on the employer half of FICA, because that money never enters their wages at all. To keep self-employed people in a comparable position, the IRS lets you shave off an equivalent portion before computing the tax.
So $80,000 of net self-employment earnings becomes $73,880 for self-employment tax purposes, and 15.3% of that is about $11,304 rather than the $12,240 a naive calculation would produce.
Where the caps and surcharges sit
The Social Security portion is capped. For 2026, it applies only to the first $184,500 of combined W-2 wages and net self-employment earnings. Cross that and the 12.4% stops — a meaningful cliff for high earners.
The Medicare portion is not capped. It applies to every dollar. And above $200,000 for single filers, $250,000 for married filing jointly, and $125,000 for married filing separately, an Additional Medicare Tax of 0.9% applies on top. Those thresholds are fixed in statute and have not been indexed for inflation since they took effect, so more people cross them every year.
If you have both a W-2 job and self-employment income, the wage base is shared: your W-2 wages count first toward the $184,500, and only the remaining room is subject to the Social Security portion of your self-employment tax.
The two deductions people miss
The first is the deduction for one-half of self-employment tax. You subtract half of what you computed as an adjustment to income on Form 1040. It is above the line, meaning you get it whether you itemize or take the standard deduction. On the $11,304 example above, that is roughly $5,652 off your taxable income.
The second is the self-employed health insurance deduction. If you pay for your own medical, dental, or qualifying long-term care coverage and are not eligible for an employer plan through your own or a spouse's job, you can generally deduct the premiums as an adjustment to income, subject to limits tied to your net self-employment earnings.
Both reduce income tax. Neither reduces the self-employment tax itself — that is computed before these adjustments.
Estimated payments, and the trap in year one
The United States runs a pay-as-you-go tax system. Employees satisfy that through withholding. Self-employed people satisfy it through quarterly estimated tax payments, generally required when you expect to owe $1,000 or more for the year.
The classic first-year mistake is not making them. You finish the year owing income tax plus self-employment tax on twelve months of profit, all due at once, plus an underpayment penalty for not having paid along the way. The penalty is calculated as interest on the shortfall for each period it was outstanding, so it accrues even if you pay in full by the April deadline.
A common defensive rule is to set aside 25% to 30% of every payment received into a separate account and never treat it as available cash. The exact right percentage depends on your bracket, your state, and your deductions — but the habit of separating it immediately is what actually prevents the problem.
What to check for your own situation
Compute your net earnings first: gross revenue minus deductible business expenses. That number, not your gross invoicing, is what both taxes are built on, which is why tracking expenses properly is worth real money.
Then apply the 92.35% factor, then the 15.3%, respecting the Social Security cap if your combined earnings approach it. Add income tax on top, computed on your net earnings after the half-of-SE-tax deduction.
This is general information about how the tax is structured, not tax advice for your situation. Entity choice in particular — whether an S corporation election would change your outcome — depends on facts that vary a great deal, and is worth a conversation with a CPA rather than a rule of thumb.